Real refractive indices of α- and β-pinene and toluene secondary organic aerosols generated from ozonolysis and photo-oxidation

Abstract

This work is the first study to investigate SOA refractive indices with sufficient resolution to begin to assess variability of SOA mr with precursor hydrocarbon, oxidation chemistry, aerosol mass concentration and possibly other factors such as temperature and aerosol aging. Aerosol m rs for SOA studied here varies from about 1.38 to 1.61, a range that is likely to have a significant impact on radiative transfer calculations. The value of the real refractive index affects the bulk radiative properties of aerosols. For instance the asymmetry parameter 〈g〉, a key parameter in radiative transfer calculations, can be affected. 〈g〉 Describes the amount of light scattered by the particles into the forward or reverse hemispheres. Using the Mie-Lorenz scattering theory, wavelength = 670 nm and mr = 1.4, 〈g〉 = 0.744 for a lognormal distribution with E(x) = 200 nm and a standard deviation of 200. Changing the mr to 1.5 produces 〈g〉 = 0.677. This change can produce an increase in the radiative forcing by at least 12% for non-absorbing particles10.